Organic diamines are generally used for chain extenders of polyurethaneurea, intermediate materials for resins, curing agents for the manufacture of epoxy resins, etc., but there has been no example of a diamine having active hydrogen at the two ends thereof and having a structure including two or more urea groups. The diaminourea compound of the present invention is a novel substance not yet disclosed in any reference and is structured with two urea groups in a molecule, as expressed by chemical formula (I), and amino groups at its two ends. When trying to synthesize this compound, the method in which one end of the diamine compound is reacted with the two ends of the diisocyanate compound to form a diaminourea compound, while urea groups are formed, may be considered. However, in a method where a diisocyanate compound is added dropwise little by little into an excess of diamine compound, the active amino groups of the reaction product react with the unreacted isocyanate groups to become higher molecular weight and it becomes difficult to remove the same as a monomer. Therefore, up to now, the physical properties and the usefulness have not been known.
In general, polyurethaneurea is obtained by causing a reaction of an excess molar amount of diisocyanate with an organic diol to synthesize an intermediate polymer with isocyanate groups at the two ends and then adding thereto an organic diamine as a chain extender to increase the molecular weight. Since an excess molar amount of the diisocyanate compound is reacted with the organic diol, the intermediate polymer (that having isocyanate groups at two ends thereof, which is called "prepolymer" hereinbelow) is comprised of an organic diol connected by the diisocyanate compound and unreacted diisocyanate compound. By adding an organic diamine there and causing a reaction between the amino groups and isocyanate groups, hard segments with urea groups are formed. The hard segments in the polymer form a hard domain by intermolecular hydrogen bonding of the urea groups. This becomes a cross-linking point for the polymer as a whole and has a major effect on the heat resistance of the polyurethaneurea.
At this time, the size of the hard segments has a distribution due to the presence of the unreacted diisocyanate compound. The minimum unit of the hard segments is formed when the prepolymer is directly connected with the added diamine compound, without being taken out by the unreacted diisocyanate compound. The structure thereof is that two molecules of the diisocyanate compound are connected with one molecule of a diamine compound (where the two molecules of the diisocyanate compound are the diisocyanate compound at the ends of the prepolymer). At this time, there are two urea groups in the structure of the minimum construction unit of the hard segment (i.e., "U2 hard" hereinbelow). The next large constitution unit next to U2 hard is that obtained by connecting the prepolymer with two molecules of the diamine compounds having one molecule of an intermediate unreacted diisocyanate compound connected therebetween, which has a structure of three molecules of the diisocyanated compound connected with two molecules of the diamine compound. At this time, there are four urea groups in the hard segment (i.e., "U4 hard" hereinbelow). Similarly, there are hard segments with successively higher molecular weights (i.e., "U6 hard", "U7 hard" . . . hereinbelow). In the conventional production method of polyurethaneurea, the minimum constitution unit of U2 hard occupies the major part of the total hard segments.
In order to improve the heat resistance of the polyurethaneurea, it is considered to introduce a greater number of urea groups in the hard segments and raise the hydrogen bonding force between molecules by making the average molecular weight of the hard segments higher. That is, the ratio of the U2 hard having a weaker intermolecule hydrogen bond force is made smaller and the ratios of the U4 hard, U6 hard . . . having a relatively high hydrogen bond force is made larger. More specifically, a diisocyanate compound is further added to the intermediate polymer and the chain is extended by a diamine compound in an equivalent amount to the isocyanate group. In this case, however, relatively high molecular weight hard segments such as U6 hard, U8 hard . . . are also formed. When the hard segments are made high molecular weight in such a way, since the solubility of U6 hard, U8 hard in a solvent is low, the viscosity stability of the polymer stock solution over time becomes poorer, when the hard segments form hard domains, and, in the worst case, gelation occurs. That is, there were limits to the control of the molecular weight of the hard segments with such a method.
In this way, with regards to the control of the molecular weight of the hard segments, which has a major effect on the heat resistant properties of the polyurethaneurea polymer, up until now the distribution of the molecular weight has not been controlled. Only the average molecular weight has been controlled and only within a limited range.
As a chain extender of a polyurethaneurea polymer, use has been made of compound including a urea group similar to the diaminourea compound according to the present invention. As an example, there has been disclosed a process for production of a heat resistant polyurethaneurea elastomer using the following formula (VI): ##STR2## wherein R.sub.1, R.sub.2, R.sub.3, and R.sub.4 each independently represent hydrogen or a C.sub.1 to C.sub.6 alkyl group, and the amino group in the formula is at the meta position and/or para position with respect to the urea (Japanese Unexamined Patent Publication (Kokai) No. 1-110520). The diaminodiphenylurea compound having the above formula (VI), however, has a low solubility in a solvent at room temperature, so when using this compound as a chain extender during the production of a polymer, a homogeneous polymerization reaction cannot be expected. Further, in the case of the above-mentioned diaminodiphenylurea compound, there is one urea group in the structure of the molecule and therefore the heat resistance cannot be said to be fully sufficient.
As a compound resembling the compound of the present invention, there is the compound having the formula (VII): ##STR3##
This compound is shown as an intermediate, in Japanese Unexamined Patent Publication (Kokai) No. 3-27351, in the production of methylenediphenylenediisocyanate and polymethylenepolyphenylenepoly(isocyanate), but since the two ends are not amino groups, but are urea groups, the reactivity is low and so this is not suitable to use as a chain extender, additive for imparting high molecular weight, curing agents, etc.
As another method for improving the heat resistance, attempts have been made in the past to make the polyurethaneurea higher in molecular weight. When just using a high viscosity stock solution increased in molecular weight during the production of a polymer (polymerization), the pressure in the pipes increases during the feeding of the solution to the molding process, the spinning stringiness becomes lower, the yarn often breaks in the spinning chimney, and other problems occur. As a method of solving these problems, the method of spinning a polymer stock solution obtained by a polymerization reaction of an intermediate polymer with an isocyanate end and an excess amount of a bifunctional and monofunctional compound having active hydrogen and the method of after-treatment of the yarn by heat to increase the molecular weight have been proposed (Japanese Examined Patent Publication (Kokoku) No. 40-3717, Japanese Examined Patent Publication (Kokoku) No.47-13789, Japanese Unexamined Patent Publication (Kokai) No. 60-14623, and Japanese Unexamined Patent Publication (Kokai) No. 60-173117). Even in these arts, however, as described on page 3 in Japanese Unexamined Patent Publication (Kokai) No. 1-170648, the viscosity of the polymer stock solution increase over time in the storage tank or feed pipes and lacks stability, so stable production was difficult. Therefore, an attempt was described of adding and mixing a low molecular weight compound (as a specific typical example, the reaction product between one mole of 4,4'-diphenylmethanediisocyanate and two moles of dialkylamine, that is, the compound having the formula (VIII): N,N-(methylenedi-4,1-phenylene)bis(diethyl)-urea) to polyurethaneurea and performing heat treatment to convert to a high molecular weight (Japanese Unexamined Patent Publication (Kokai) No. 59-129257 and Japanese Unexamined Patent Publication (Kokai) No. 1-170648) ##STR4##
However, a polyurethaneurea shaped article made by the known art using a compound having the formula (VIII) was unsatisfactory in the following points:
(1) The effect of improvement of the elastic functions and heat resistance is still insufficient.
(2) The knot strength is low.
(3) During spinning, the yarn often breaks inside the spinning chimney (stringiness of spinning stock solution is low).
Furthermore, the aromatic diurea compound having the chemical formula (VIII) of the known art, unlike with the following formula (I) of the present invention, does not have active hydrogen groups at the two end groups and is low in chemical activity. Therefore, these are not suitable as a chain extender of polyurethaneurea, additives for high polymerization, curing agents for epoxy resins, etc.